It is known that the compressor of an aircraft turbine engine may "stall" under certain conditions. It is also known that bleeding high-pressure air from the compressor can increase the compressor's range of stable operation, averting the onset of compressor stall and/or aiding in recovery from compressor stall. Such a stability bleed system is typically provided by a bleed port at a desired compressor stage and a bleed duct leading from the bleed port to an exit opening discharging into the engine fan stream downstream of the fan nozzle.
A problem with known stability bleed systems is that substantial noise is generated where the stream of bleed air discharges into the fan stream. The principal object of the present invention is to provide an effective noise suppressor for a stability bleed air duct. It is also an object of the invention to provide such a noise suppressor which does not create significant back pressure during low power operation of the engine.
The prior art shows compressor bleed ducts with gradually increasing cross-sectional areas to diffuse the air flow and reduce noise. The problem with these systems is that stability bleed air often has a pressure such that the velocity at the outlet is supersonic. Increasing the cross-sectional area of a duct carrying such an air stream may actually cause an increase in generated noise.